Trying To Understand VI

[Ken2]

Viscosity index is the relative change in viscosity of the oil from 40°C to 100°C. It does not precisely detail what happens at other temperatures.

The numbers Caterham posted are from the definitions of each group of base oil. There are other requirements for the base oil group classifications relating to saturates (oxygen atoms replaced by hydrogen atoms on the oil molecule) and sulfur content:
http://www.infineum.com/Documents/API/SAE Viscosity Grades for Engine Oils 2010.pdf

A finished oil product with a higher viscosity spread will by definition have a higher VI than one with a lower visc spread, i. e., a 5w30 will always have a higher VI than a 10w30.

As said above, don't put too much effort into specs. Pick an oil that the engine designer spec'ed for your engine, and look at how the choice of oils performed in engines based on used oil analyses.

 

[CATERHAM]

Mitch you said:

" VII is simply a number that represents the quotient of another pair of numbers. Those other numbers are much more useful in understnading oil and lubrication than the VII number.
If we labled oil by actual viscosities instead of grade weights the picture would be more clear. Then one could actually look for an oil that was 10 cSt at 240dF where his engine runs."

I'd agree if it wasn't for the fact that the kinematic viscosity measure of doesn't correlate well with operational viscosity like the HTHSV measure does. Consiquently the VI being a rate of change measure is more valuable than the two KV spec's it is derived from.
In other words, in comparing two oils with the same or close HTHSVs, the oil with the higher VI will be lighter on start-up at all temp's, and the lower the temperature the lower the initial start-up viscosity (lower oil pressure) of the oil with the higher VI.

 

[oiltard]

Okay, I'm fascinated by this exchange and would like to know if I'm getting the general idea. Can someone confirm whether this general line of thinking is on track?

The plot of viscosity vs. temperature is a curve rather than a linear function. But basically I'm thinking of VI as the slope of the function through the 40C and 100C temperature points.

Caterham's argument is that you should consider this "slope" and operating viscosity (better represented by HTHSV than KV100) as the most pertinent available data for viscosity determination rather than the grade on the bottle's label. So you should choose the lightest oil appropriate to your application at op temp (HTHSV?), and then pick the highest VI option of those because it will thicken the least as temperature decreases from operating temperature, and therefore flow the best from startup.

Am I close?

 

[CATERHAM]

That's correct.
I'll also add that viscosity change with temperature is virtually linear at high temp's, that is from 150C down to 100C and even further with light 20wt oils. It's just one of the reasons why one can rely on the HTHSV and largely ignore the KV100 spec'.

 

[jstutz]

download the .xls and look at the curves. there are three stand oil plotted in there already and you could change them to anything you want. I believe it will help in your understanding.

 

[Lyman]

I want to thank you all for the Monday evening education. Now where can I find that Sustina again?

Just kidding.

 

[Doc Holiday]

Don't put to much on VI. Remember VI can be "tricked" with additives. So can Pour Point and so on. But of the spec, flash point can not be "tricked" with additives. Notice that all Synthetics have a high flash point (those worth their salt anyway). VI #'s in synthetics are high also. In conventional oil the VI can be high..but due to VII that quickly "shear" down. The better the base stock the high the VI and less VII has to be added. Always remember that the more additives that are in the bottle, means less "oil" in the bottle.

 

[Dupree]

Caterham excellent information as usual, would you care to list the over 200 Vi oils out there curiosity has gotten the better of me

 

[CATERHAM]

Off the top of my head; what's available in NA:

Sustina 0W-20, V1 229
Sustina 0w50, VI 200+ (haven't found the exact spec')
Castrol Edge SM GF-4 0W-20, VI 220 (if you can still find it, SN version is only 162)
CAM 2 Synavex SM GF-4 0W-20, VI 206 (SN version is something like 179 IIRC)
Toyota 0W-20, VI 216
Idemitsu SM GF-4 0W-20, VI 197-200
Supplied to:
Honda USA (but not currently)
Honda/Acura Cdn
Mazda
Mitsubishi
Subaru (but not currently astheir getting the 169 VI SN GF-5 version)
Red Line 0W-40, VI 197

 

[cp3]

Originally Posted By: jstutz
download the .xls and look at the curves. there are three stand oil plotted in there already and you could change them to anything you want. I believe it will help in your understanding.


^do this, he is right. This is the sheet I have been using for a while now, good stuff.

I think Caterham has listed them before(I'll post the link if I come across it), there isn't many with the Toyota 0w20 being the easiest/cheapest to get.

 

[cp3]

Wow...I'm quick eh!

 

[dparm]

Originally Posted By: CATERHAM
Off the top of my head; what's available in NA:

Sustina 0W-20, V1 229
Sustina 0w50, VI 200+ (haven't found the exact spec')
Castrol Edge SM GF-4 0W-20, VI 220 (if you can still find it, SN version is only 162)
CAM 2 Synavex SM GF-4 0W-20, VI 206 (SN version is something like 179 IIRC)
Toyota 0W-20, VI 216
Idemitsu SM GF-4 0W-20, VI 197-200
Supplied to:
Honda USA (but not currently)
Honda/Acura Cdn
Mazda
Mitsubishi
Subaru (but not currently astheir getting the 169 VI SN GF-5 version)
Red Line 0W-40, VI 197



Don't forget Renewable Lube's 0w30 at 193 and their 5w40 at 188.

 

[CATERHAM]

dparm, I wasn't going to go that low.
Then I'd have to include:
M1 R 0w50, VI 189
Quaker State 5w50, VI 193 IIRC possibly other GP III 5W-50s.
ENEOS 0w50, VI 192
etc

 

[jstutz]

Originally Posted By: cp3
Originally Posted By: jstutz
download the .xls and look at the curves. there are three stand oil plotted in there already and you could change them to anything you want. I believe it will help in your understanding.


^do this, he is right. This is the sheet I have been using for a while now, good stuff.

I think Caterham has listed them before(I'll post the link if I come across it), there isn't many with the Toyota 0w20 being the easiest/cheapest to get.


Glad someone is getting some use out of it. I thought about keeping it updated with current specs for popular brands but since i posted it here probably two years ago I think you are only the third person to actually download it and used it. I thought with all of the oil enthusiasts here, and how often folks were referred to widman, more people would be interested in such a tool. Throw some Gear oil numbers in there for fun. Its crazy how thick something like 90w140 gets as it gets colder.

 

[yonyon]

I recently saw some 80w90 that was in continuous use since 1992 drain as about 65 degrees F. I'm assuming it was no longer in grade. It didn't so much drain in a stream as in gobbets. When you get to gobbets is that considered below the pour point?